The commencement of the developmental cycle and of the infection of man, is the sporozoites (fig. 80, _1_) which are passed into the blood of a person by the bite of an infected mosquito. Prior to this the parasites collect in the excretory ducts of the salivary glands (fig. 80, _27_) of the _Anopheles_. The sporozoites are elongate and spindle-shaped, 10 µ to 20 µ long and 1 µ to 2 µ broad, with an oval nucleus situated in the middle. They are able to glide, perform peristaltic contractions, or curve laterally. Schaudinn has studied the penetration of the red blood corpuscles (fig. 80, _2_) by the sporozoites in the case of the living tertian parasite. The process takes forty to sixty minutes in drawn blood. After its entrance the parasite, which is now called a trophozoite, contracts, and becomes an active amœbula (fig. 80, _3_). It develops a food vacuole and grows at the expense of the invaded blood corpuscle (fig. 80, _4_), which is shown by the appearance of pigment granules (transformed hæmoglobin) in it. When the maximum size is attained, multiplication by schizogony (fig. 80, _5_-_7_) begins with a division of the nucleus, which is followed by further divisions of the daughter nuclei, the number of which varies up to 16 or even 32, depending on the species of the parasite. Then the cytoplasm divides into as many portions as there are nuclei, the result being a structure suggestive of the spokes of a wheel or of a daisy, the centre of the resulting rosette being occupied by dark pigment. Finally, the parts separate from one another, leaving behind a residual body containing the pigment, and the daughter forms issue into the blood plasma as merozoites (fig. 80, _7_). They are actively amœboid (fig. 80, _8_) and soon begin to enter other blood corpuscles of their host, for the entry into which thirty to sixty minutes are necessary, according to Schaudinn’s observations.[197] [197] It should be remembered that some authors (Laveran, Argutinsky, Panichi, Serra) argue against the intra-globular position of malarial parasites and state that they only adhere outwardly to the red blood corpuscles. These views have recently been revived by Mary Rowley-Lawson, and she states that the malarial parasite is “extracellular throughout its life-cycle and migrates from red corpuscle to red corpuscle destroying each before it abandons it.” (_Journ. Exper. Med._, 1914, xix, p. 531.) Here they behave like sporozoites which previously entered and again produce merozoites. This process is repeated until the number of parasites is so large that, at the next migration of the merozoites, the body of the person infected reacts with an attack of fever,[198] which is repeated with the occurrence of the next or following generations. [198] The incubation period, that is, the time between infection and the first attack of fever, is ten to fourteen days; with severe infection fewer days (minimum 5 to 6) are needed.